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e-.c. uaterand adding 45 c.c. absolute alcohol. An accurately
\v^ii-ine(l i|uantily (0*3 u'ogram ) of substance is inlroducecl in a
cjinall weighing tube into the distilling flask and 15 c.c. of strong
l^yclriodic acid (acid of sp. gr. 17 for Xeisel's estimations can be
purchased). When the apparatus has been carefully fixed
tog-ether the glycerol bath is heated to 130140''and a slow
current of carbon dioxide (two bubbles a second) is passed
through the apparatus. The temperature of the glycerol bath
js slowly raised until the hydriodie acid begins to boil gently. A
%vhite deposit (a compound of silver iodide and nitrate) begins to

form on the surface of the first flask and gradually settles to
tlie bottom, but usually only a trace appears in the second vessel.
The operation is generally completed in one hour; but before
slopping the process it is advisable to test the vapour passing
through by removing the flasks and attaching the small bent
U-ttibe (shown in the Fig. and containing a little alcoholic silver
nitrate solution) to the end of the side tube. If in the course of
ten minutes no turbidity appears, the operation may be con-
sidered at an end, otherwise it is necessary to connect up the
flask and continue the heating for another twenty minutes.
About 50 c.c. of water are heated to boiling in a beaker (250